Agent Skills: Modern Rails 8 Architecture Patterns

Modern Rails 8 Architecture Patterns

Architecture Decision Tree

Where should this code go?
|
+- View/display formatting?       -> Presenter (@presenter-agent)
+- Complex business logic?        -> Service Object (@service-agent)
+- Complex database query?        -> Query Object (@query-agent)
+- Shared behavior across models? -> Concern (/rails-concern skill)
+- Authorization logic?           -> Policy (@policy-agent)
+- Reusable UI with logic?        -> ViewComponent (@viewcomponent-agent)
+- Async/background work?         -> Job (@job-agent, /solid-queue-setup skill)
+- Complex form (multi-model)?    -> Form Object (@form-agent)
+- Transactional email?           -> Mailer (@mailer-agent)
+- Real-time/WebSocket?           -> Channel (/action-cable-patterns skill)
+- Data validation only?          -> Model (@model-agent)
+- HTTP request/response only?    -> Controller (@controller-agent)

Layer Responsibilities

| Layer | Responsibility | Should NOT contain | |-------|---------------|-------------------| | Controller | HTTP, params, response | Business logic, queries | | Model | Data, validations, relations | Display logic, HTTP | | Service | Business logic, orchestration | HTTP, display logic | | Query | Complex database queries | Business logic | | Presenter | View formatting, badges | Business logic, queries | | Policy | Authorization rules | Business logic | | Component | Reusable UI encapsulation | Business logic | | Job | Async processing | HTTP, display logic | | Form | Complex form handling | Persistence logic | | Mailer | Email composition | Business logic | | Channel | WebSocket communication | Business logic |

When NOT to Abstract

| Situation | Keep It Simple | Don't Create | |-----------|----------------|--------------| | Simple CRUD (< 10 lines) | Keep in controller | Service object | | Used only once | Inline the code | Abstraction | | Simple query with 1-2 conditions | Model scope | Query object | | Basic text formatting | Helper method | Presenter | | Single model form | form_with model: | Form object | | Simple partial without logic | Partial | ViewComponent |

When TO Abstract

| Signal | Action | |--------|--------| | Same code in 3+ places | Extract to concern/service | | Controller action > 15 lines | Extract to service | | Model > 300 lines | Extract concerns | | Complex conditionals | Extract to policy/service | | Query joins 3+ tables | Extract to query object | | Form spans multiple models | Extract to form object |

See /extraction-timing skill for detailed extraction guidance.

Core Patterns

Skinny Controllers

# GOOD: Thin controller delegates to service
class OrdersController < ApplicationController
  def create
    result = Orders::CreateService.call(user: current_user, params: order_params)
    if result.success?
      redirect_to result.data, notice: t(".success")
    else
      flash.now[:alert] = result.error
      render :new, status: :unprocessable_entity
    end
  end
end

Result Objects for Services

All services return a consistent Result object:

Result = Data.define(:success, :data, :error) do
  def success? = success
  def failure? = !success
end

Multi-Tenancy by Default

# GOOD: Scoped through account
def index
  @events = current_account.events.recent
end

Rails 8 Specific Features

| Feature | Purpose | Skill/Agent | |---------|---------|-------------| | Authentication | has_secure_password generator | /authentication-flow | | Background Jobs | Solid Queue (database-backed) | /solid-queue-setup, @job-agent | | Real-time | Action Cable + Solid Cable | /action-cable-patterns | | Caching | Solid Cache (database-backed) | /caching-strategies | | Assets | Propshaft + Import Maps | (built-in) | | Deployment | Kamal 2 + Thruster | (built-in) |

Testing Strategy by Layer

| Layer | Test Type | Focus | |-------|-----------|-------| | Model | Unit | Validations, scopes, methods | | Service | Unit | Business logic, edge cases | | Query | Unit | Query results, tenant isolation | | Presenter | Unit | Formatting, HTML output | | Controller | Request | Integration, HTTP flow | | Component | Component | Rendering, variants | | Policy | Unit | Authorization rules | | System | E2E | Critical user paths |

New Feature Checklist

1. Model - Define data structure (@migration-agent, @model-agent)
2. Policy - Add authorization rules (@policy-agent)
3. Service - Create for complex logic (@service-agent)
4. Query - Add for complex queries (@query-agent)
5. Controller - Keep it thin (@controller-agent)
6. Presenter - Format for display (@presenter-agent)
7. Component - Build reusable UI (@viewcomponent-agent)
8. Mailer - Add transactional emails (@mailer-agent)
9. Job - Add background processing (@job-agent)

References

• See layer-interactions.md for layer communication patterns
• See service-patterns.md for service object patterns
• See query-patterns.md for query object patterns
• See error-handling.md for error handling strategies
• See testing-strategy.md for comprehensive testing